The National Institute for Health and Care Excellence (NICE, or the Institute) provides guidance to the NHS in England on the clinical and cost effectiveness of selected new and established technologies. The Institute undertakes appraisals of health technologies at the request of the Department of Health. Guidance produced by the Institute on health technologies is also applied selectively in Northern Ireland, Scotland and Wales.

The purpose of this document is to provide an overview of the principles and methods of health technology assessment and appraisal within the context of the NICE appraisal process. It describes key principles of appraisal methodology and is a guide for all organisations considering submitting evidence to the technology appraisal programme of the Institute.

The Institute regularly reviews its processes and methodology. This document updates the 'Guide to the methods of technology appraisal' published in 2008. This document does not provide a detailed description of the processes used to develop guidance. Information on the process of conducting a technology appraisal is available in 2 companion documents to this guide: Guide to the multiple technology appraisal process and Guide to the single technology appraisal process. A review of these documents is currently underway; further information will be available on the NICE website.

Because the methodology of technology appraisal continues to develop, there remain areas of controversy and uncertainty, particularly in relation to the methods of cost-effectiveness analysis. However, it is important that the methods used to inform the Appraisal Committee's decision-making are consistent. For this reason, the Institute has adopted the approach of using a 'reference case' for cost-effectiveness analysis; this was chosen as most appropriate for the Appraisal Committee's purpose.

The Institute sponsors research into the methods of technology appraisal and welcomes suggestions to the Director of the Centre for Health Technology Evaluation for both primary and secondary research that might lead to improvements in methods and make subsequent editions of this document more helpful.

In August 2017, NICE issued a position statement on the use of the EQ‑5D‑5L valuation set. Companies and academic groups should refer to this statement.